This invention concerns itself with aqueous magnetic coating formulations. It is desirable at times to use aqueous formulations in place of organic formulations for the latter use expensive and toxic flammable solvents, which must be captured upon drying of the magnetic formulation to prevent air pollution. Furthermore, there have been a number of recent developments in improving magnetic aqueous formulations, which make them attractive as substitutes for organic-based coatings generally.
Notwithstanding the inherent advantages of employing aqueous magnetic coating formulations, such coatings have not, to date, replaced organic formulations commercially. One reason for the lack of success is that prior art magnetic coating layers employ emulsifiers or dispersants, which do not form an adequate bond between the magnetic pigments incorporated in the coatings and the water-based binders. As a result, the coatings become brittle as the emulsifiers exude to the coating surface. A further disadvantage of the emulsifiers of the prior art, such as TAMOL 731 which is a sodium salt of a carboxylate sold by Rohm & Haas and TRITON X-100 which is an alkyl aryl polyether alcohol also offered from Rohm & Haas, is their tendency to not only diffuse to the surface of the magnetic coating over time, but also cause the aqueous formulation to foam during preparation. The antifoaming agents employed by the prior art do not completely remedy the problem, particularly in the preparation of high viscosity magnetic coating compositions.
Yet another problem in prior art aqueous-based magnetic coating compositions is the tendency of the magnetic particles and other pigments, such as carbon, to flocculate. The use of improved dispersion agents can not only avoid the flocculation problem, but also stabilize the magnetic powder and other pigments incorporated in the composition.
It is thus an object of the present invention to provide an improved aqueous magnetic coating composition without the drawbacks of prior art compositions.
It is yet another object of the present invention to employ improved dispersing agents in aqueous magnetic coating compositions to avoid those disadvantages outlined above.
These and other objects of this invention will be more fully appreciated when considering the following disclosure.